Towards a Theoretical Framework for Usability

Keith A. Butler

Math and Computing Technology
Boeing Phantom Works

Date: Friday, February 11, 2005
Place: Engineering Sciences Building, Room 2001
Time: 2:00 pm — 3:00 pm (Refreshments served at 1:30 pm)

Abstract:
Conventional definitions of usability are holistic and confound it the difficulty of user work and the functionality of supporting applications. This deficiency has serious disadvantages for a theory of human-computer interaction, and practical limitations on the practice of usability engineering. We propose a distributed-cognition framework for usability in terms of the characteristics of the mental work that users must perform, which has separate, independent components for: 1) the intrinsic difficulty of the work; and 2) the user effort for accomplishing it with a given interface. Some of this user effort is not intrinsic to the nature of the work, and is only present due to the way the application was implemented. We call that non-intrinsic activity overhead. We illustrate and test the framework by demonstrating how an ontology for the well-studied Tower of Hanoi puzzle was analyzed to define two isomorphic user interfaces for solving the problem, which varied overhead independently from problem difficulty in controlled experiment. The results of the data confirmed the framework’s prediction. Overhead was only 31% of total user actions but accounted for 93% of the variance in solution-time. We discuss the implications of our findings for a theory of usability, a practical measurement model for usability, and challenges for widespread application.

KEITH BUTLER is a Boeing Technical Fellow in the Math & Computing Technology, where he is responsible for the core technology area of human-computer interaction. He completed his PhD in cognitive psychology at Tufts University in 1980 and began working at Bell Telephone Labs, where he developed user-centered methods and prototypes for maintenance information systems. Working with John Bennett and John Whiteside, he was one of the originators of Usability Engineering. He is past chair for the ACM SIGCHI conference on computer-human interaction, and currently serves on the steering committee for software product usability at U.S. National Institute for Standards & Technology.

Host: Mary Hegarty, Professor of Psychology